better docstrings (#144)

* first example of returns statement in docstring

* added a some return statements for pandas API

* last return statements in pandas input

* added returns to bdio docstrings

* few returns statements added to docstring

* finished docstrings for hadrons submodule

* also finished docstrings for json submodule

* finished misc submodule

* added returns in docstrings in openqQCD

* made some cosmetic chanes to dostrings

* added return nad return statement in docstring

* linting

* Improved docstrings of mpm, fits, roots, misc to have return statements

returns added for misc.py

returns added for mpm.py

reutrns added for fits.py

* linting...

* Some polishing of docstrings

pyerrors/input/pandas.py

@@ -22,6 +22,10 @@ def to_sql(df, table_name, db, if_exists='fail', gz=True, **kwargs):
         How to behave if table already exists. Options 'fail', 'replace', 'append'.
     gz : bool
         If True the json strings are gzipped.
+
+    Returns
+    -------
+    None
     """
     se_df = _serialize_df(df, gz=gz)
     con = sqlite3.connect(db)
@@ -41,6 +45,11 @@ def read_sql(sql, db, auto_gamma=False, **kwargs):
     auto_gamma : bool
         If True applies the gamma_method to all imported Obs objects with the default parameters for
         the error analysis. Default False.
+
+    Returns
+    -------
+    data : pandas.DataFrame
+        Dataframe with the content of the sqlite database.
     """
     con = sqlite3.connect(db)
     extract_df = pd.read_sql(sql, con, **kwargs)
@@ -62,6 +71,10 @@ def dump_df(df, fname, gz=True):
         Filename of the output file.
     gz : bool
         If True, the output is a gzipped csv file. If False, the output is a csv file.
+
+    Returns
+    -------
+    None
     """
     out = _serialize_df(df, gz=False)
 
@@ -88,6 +101,11 @@ def load_df(fname, auto_gamma=False, gz=True):
         the error analysis. Default False.
     gz : bool
         If True, assumes that data is gzipped. If False, assumes JSON file.
+
+    Returns
+    -------
+    data : pandas.DataFrame
+        Dataframe with the content of the sqlite database.
     """
     if not fname.endswith('.csv') and not fname.endswith('.gz'):
         fname += '.csv'